The present invention relates to a retractor (winding device) for use in a seat belt device, and particularly to an improved retractor with a clamping mechanism which directly holds a webbing between opposite parts thereof in a vehicle emergency, thereby to minimize the amount of draw-out of the webbing.
Conventionally, a seat belt device has been used in a vehicle to protect an occupant against collision shocks. The seat belt, when operated, restrains the occupant in a seat. Some retractors are provided with an emergency locking mechanism and a clamping mechanism. In a vehicle emergency, such as a collision, the emergency locking mechanism locks the rotation of the winding shaft with a webbing wound thereon in the webbing draw-out direction, and the clamping mechanism directly holds the webbing between opposite parts thereof to prevent the draw-out of the seat belt because of the tightening of the seat belt.
In a vehicle emergency, it is conceivable that the webbing held by the clamping mechanism possibly would receive a force greater than the breaking strength of the webbing. Specifically, if a strong tensile force to draw out the webbing is further applied to the retractor in which the clamping mechanism has prevented the seat belt from drawing out by holding the webbing, there is a possibility that a force would be concentrated on the webbing holding portion.
The retractor with a simple clamping mechanism functioning so as to prevent the seat belt from drawing out by holding the webbing, operates as indicated by a dotted line in FIG. 38, in the emergency. As time passed immediately after a vehicle collision, a tension of the webbing increases. When a shock by the collision is extremely large, an abrupt deceleration acts on the body of the occupant. As a result, a load by the seat belt to the occupant can also be large.
In order to avoid the above problems, there is another proposal of the retractor with an improved clamping mechanism. According to this retractor, in an early stage where the tensile force acts on the webbing upon a collision shock applied smaller than a predetermined value, the clamping mechanism is operated to prevent the draw-out of the seat belt, whereby the body of the occupant is reliably restrained to the seat. Thereafter, the tensile force acting on the webbing exceeds the predetermined value. At this time, the operation of the clamping mechanism is removed to allow the webbing to be drawn out a predetermined amount thereof, and the deceleration in the body of the occupant is lessened. As a result, the occupant is protected from the collision.
Various types of the retractors with clamping mechanism are proposed, for example, in U.S. Pat. Nos. 5,154,368 and 5,299,854, and Unexamined Japanese Utility Model Publication No. Hei. 4-43550. The disclosed retractor uses a clamp removing mechanism which removes the clamping force in such a manner that when a tensile force exceeding a predetermined value is applied to the webbing, a part of the rotary holding member holding the webbing is plastically deformed, or a part of a case (retractor base) rotatably supporting an end of the rotary holding member or a part of the shaft is plastically deformed or broken. Thus, a deceleration acting on the body of the occupant is lessened to reliably protect the occupant from a collision shock in such a manner that in an emergency, a predetermined amount of the extension of the seat belt is allowed by removing the clamping mechanism in operation.
As for the clamping mechanism, the clamp member rotatably supported at an end of the retractor base holds the webbing to prevent the extension of the seat belt as mentioned above. On the other hand, there is another clamping mechanism. In this mechanism, to prevent the extension of the seat belt, a wedge-shaped clamp member holds the webbing so that the clamp member bites into a space between the base back plate and a slide surface of a guide member fixed to the retractor base. Because of differences of the constituent components and parts, such a clamping mechanism cannot be applied to the various clamp removing mechanisms.
U.S. Pat. No. 5,242,213 and Unexamined Japanese Utility Model Publication No. Hei. 4-43551 disclose clamp removing mechanisms that are applicable to the clamping mechanism using the wedge-shaped clamp member.
In the clamp removing mechanisms disclosed, a belt retracting device (retractor) and a webbing clamping device (clamping mechanism) are connected to each other by a connecting device, which allows a limited motion of the webbing clamping device. At the instant that a predetermined load value is reached, the webbing clamping device is plastically deformed to move apart from the belt retractor. When a webbing tensile force exceeding a predetermined load value acts on the webbing clamping device, the connecting device is broken to remove the holding of the webbing by the webbing clamping device.
In the construction of the clamp removing mechanism disclosed in Unexamined Japanese Utility Model Publication No. Hei. 4-43551, a holding portion (teeth portion) provided on the surface of a holding device where it faces the webbing is capable of being sheared by a tensile force acting on the webbing. When a tensile force exceeding a predetermined value is applied to the webbing, the holding portion is sheared, to remove the webbing from being held by the holding device.
The retractor with the clamping mechanism, disclosed in Unexamined Japanese Utility Model Publication No. Hei. 4-43551, is shown in FIGS. 39 through 42. In case of emergency, for example, when a vehicle collision takes place, the retractor operates in the following way. An emergency locking mechanism 124 locks a winding shaft 123 with a webbing 126 (serving as a seat belt) wound thereon, thereby preventing the draw-out of the webbing 126 that is based on the rotation of the winding shaft 123. At the same time, a clamping mechanism 125 holds the webbing 126 that has been drawn out onto a base back plate 121 of the retractor base 120, from the winding shaft 123. With the holding, the webbing 126 left on the winding shaft 123 is prevented from drawing out because of the tightening of the webbing 126.
The clamping mechanism 125 includes a clamp shaft 111 supported at both ends thereof by a pair of side walls 122 of the retractor base 120, a clamp holder 112 which is supported swingably about the clamp shaft 111 and moves along the webbing 126 on the base back plate 121 of the retractor base 120, and a clamp member 113 attached to the top of the clamp holder 112. In an emergency, the clamp holder 112 is swung in the direction of an arrow B (FIG. 39), thereby to press the clamp member 113 against the webbing 126. In this state, the webbing 126 is compressed between the clamp member 113 and the base back plate 121, so that the webbing is locked there. In this way, the webbing 126 is prevented from being drawn out.
The clamp member 113 has a semicircular shape as shown also in FIG. 40. Support shafts 114, rotatably supported by the clamp holder 112, are extended from both sides of the clamp member 113. The clamp member 113 is rotatably attached to the top end of the clamp holder 112 in a state that a semicircular outer surface 115 thereof is located close to the clamp holder 112. A flat surface of the clamp member 113, which faces the webbing 126, has a number of holding portions 116 (clamp teeth) formed thereon. As also shown in FIG. 40, these holding portions have sharpened portions at ends thereof to prevent the webbing from drawing out by sticking the sharpened portions into the webbing when the holding portions 116 are pushed toward the webbing 126. The strength and the size of the holding portions 116 are selected such that when a load exceeding a predetermined value acts on the sharpened portions of the holding portions 116, these sharpened portions of the holding portions are sheared, so that the webbing is removed from its held state.
The clamping mechanism 125 shown in FIGS. 39 and 40 operates in the following way. In an early stage of an emergent collision, the clamp member 113 is pressed against the webbing 126 to stick the holding portions 116 into the webbing 126. Thus, the webbing 126 is placed in a locked state. In this state, it cannot be drawn out. When after the webbing is arrested, a tensile force acting on the webbing is increased to exceed a predetermined value by an inertial energy of the occupant, for example, the holding portions 116 are sheared to release the webbing from its locked state. Accordingly, the shock to the body of the occupant, that results from the webbing tightly holding the occupant, is lessened.
FIG. 41 shows a state of the retractor in which the clamping mechanism 125 operates to stick the holding portions 116 of the clamp member 113 into the webbing 126, thereby locking the webbing. FIG. 42 shows another state of the retractor in which after the webbing is arrested, the tensile force acting on the webbing reaches a predetermined value or greater, so that the holding portions 116 are sheared to release the webbing from its locked state. In this case, the upper half portions 117 of the holding portions 116 are left in the webbing 126.
A kinetic energy absorbing mechanism based on the plastic deformation is disclosed in Unexamined Japanese Utility Model Publication No. Hei. 4-62255. In this mechanism, a plastic deformation of the folded portions of a U-shaped plate absorbs kinetic energy.
In the retractor with a clamp removing mechanism disclosed in U.S. Pat. No. 5,242,213, when the tensile force of the webbing exceeding a predetermined value acts on the webbing holding device, the connecting device is broken and the webbing holding device moves apart from the belt retractor. In the retractor with a clamp removing mechanism disclosed in Unexamined Japanese Utility Model Publication No. Hei. 4-43551, when the tensile force of the webbing exceeding a predetermined value acts on the clamp member, the holding portion is sheared, so that the webbing holding force is instantaneously removed.
In these clamping mechanisms, at the instant that the webbing holding force is removed, the webbing put on the winding shaft is tightened. Accordingly, the webbing is abruptly drawn out after the removal of the holding force, and a tensile force acting on the webbing abruptly decreases. Thereafter, the rotation of the winding shaft in the webbing draw-out direction is locked by the emergency locking mechanism, and the tensile force of the webbing abruptly increases again if circumstances require.
The retractor of Unexamined Japanese Utility Model Publication No. 4-43551 is constructed such that when the tensile force acting on the webbing reaches a predetermined value or greater after the webbing is held by the clamping mechanism 125, the webbing is released from its holding state. In the retractor thus constructed, a variation of the tensile force of the webbing after the collision takes place is as indicated by a two-dot chain line in FIG. 38. As shown, when the tensile force reaches a predetermined value P1, the draw-out of the webbing caused by the tension therein starts and the tensile force decreases. When the draw-out of the webbing stops, the tensile force of the webbing increases again from a tension P2 at that time and reaches a tension P3 that is greater than the tension P1. Accordingly, the maximum tension acting on the seat belt can be controlled to be smaller than that by a retractor which uses a clamping mechanism without a clamp removal function.
To properly reduce the maximum tension acting on the seat belt, a timing to remove the holding of the webbing by shearing the holding portions 116 must be made to exactly correspond to the tensile force acting on the webbing. Additionally, to effectively reduce collision shocks acting on the occupant in case of emergency, it is necessary to reduce the maximum tension acting on the seat belt, to avoid abrupt increases and decreases of the tension in the webbing, and to minimize a variation of the tension.
In the construction of the conventional clamping mechanism 125, the timing (webbing tension) of shearing the holding portions 116 tends to vary depending on shock operating conditions (deceleration conditions). Therefore, it is very difficult to make the timing of the holding removal correspond to the tension acting on the webbing. As a consequence, it is difficult to obtain the shock absorption performances as designed.
The causes of this problem are as follows. As shown in FIG. 43, two forces acts on the holding portions 116 of the clamp member 113 when it is pressed against the webbing 126. One of the two forces is a shearing force f1 by the tension in the webbing 126, and the other is a reaction force f2 to the pushing force that is applied to the webbing 126 by the swing motion of the clamp holder 112. It is estimated that the resultant force f3 of these forces f1 and f2 would actually break the holding portions 116. In the above-mentioned clamping mechanism 125, after the webbing is compressed, the operation of pushing the webbing against the base back plate through the swing motion of the clamp holder 112 continues until the holding portions 116 are broken by the resultant force f3. Under this condition, the reaction force f2 continuously increases as a tensile force acting on the webbing 126 increases. An increasing rate of the reaction force f2 varies depending on an increasing rate of the tensile force and the like. Due to these facts, the reaction force f2 greatly influences the resultant force f3 to actually break the holding portions 116.
According to the construction of the conventional clamping mechanism 125 as mentioned above, the increase and decrease of the tensile force are alternately repeated at short time intervals as shown also in FIG. 38. Therefore, a tension acting on the seat belt is also sharply increased and decreased, so that the amplitude of the tension variation would also be great.
Further, in those clamp removing mechanisms, when a vehicle collision takes place and the retractor operates to restrain an occupant, the energy absorption immediately after the clamp removal is inefficient. The increase of the load which follows the decrease thereof is great. Its rising slope is sharp. Consequently, the kinetic energy of the occupant is insufficiently absorbed, and reduction of a collision shock applied to the occupant is also insufficient.
When the energy absorption mechanism disclosed in Unexamined Japanese Utility Model Publication No. Hei. 4-62255 is incorporated into the retractor, a folded portion of a U-shaped member is formed on the lower stay extending downward from the retractor base. The main body of the retractor is fixed to a vehicle body with a casing secured to the panel of the vehicle body inserted therebetween. If a webbing tensile force exceeding a predetermined value acts on the retractor, the folded portion is plastically deformed. As a result, the main body of the retractor moves upward. Because of the extension of the upper stay upward from the retractor base, it is difficult to fix it to the vehicle body. In this respect, its reliability of mounting on the vehicle body is poor. Additionally, there is a possibility that additional vibrations are easily generated in the main body of the retractor that is fixed to the body panel only by the lower stay.